The present invention relates to a recognition and management system that is more particularly intended for electrochemical cells, which cells are generally associated together to form a battery.
Using electrochemical cells, in particular in portable applications, poses the problem of how to find out accurately the available capacities of the cells and the degree of aging thereof, since the performance levels of the cells decrease with use. Mere voltage measurement does not enable the charge level of an electrochemical cell to be determined correctly.
With a battery of storage cells used in a portable video camera, a solution that has been proposed is to monitor the state of charge by taking a coulometric measurement which takes self-discharge into account. The apparatus used to perform such monitoring and associated with the battery includes a 4-bit microcontroller, and it is capable of detecting the end of charging and the end of discharging so as to establish a set point. But that solution solves the problem posed in part only, and that apparatus involves considerable extra cost.
Furthermore, in theory, it is possible to make applications operate with electrochemical cells of different types or origins. In practice, this poses numerous problems due to different electrical characteristics (voltage, internal impedance, etc.), and often it results in a reduction in the performance levels of the electrochemical cell, and sometimes it does not even work at all. For a rechargeable electrochemical cell, the consequences are much more serious if the application is a charger, because a rechargeable electrochemical cell that is not charged properly may be rapidly degraded, thereby giving rise to major risks with respect to safety (explosion, fire, etc.).
To avoid charging primary electrochemical cells, mechanical identifying means are provided that are recognized by the charger and that inhibit charging. Identifying means (resistors, diodes, etc.) for identifying the type of cell so as to adapt the charging conditions thereto are also mentioned, e.g. in British Patent Applications GB-2 219 151 and GB-2 251 515, or in U.S. Pat. No. 5,200,689. But that technique can only be used for a family of products coming from the same manufacturer.
Patent JP-4 255 431 proposes a charger that is capable of taking a voltage measurement to determine the type of rechargeable electrochemical cell constituting the battery, so as to apply the appropriate charging current. That method is applicable only to rechargeable electrochemical batteries in which the number of cells connected in series is known, and which require slow charging. By a mere voltage measurement, it is impossible to determine whether or not the rechargeable electrochemical cell is designed to withstand fast charging.
European Patent Application EP-0 448 755 proposes to store information about the type of the cell in a nonvolatile RAM. That memory may be modified or erased intentionally or accidentally, which means that the cell can no longer be used under appropriate conditions.
Moreover, most known systems, e.g. such as the system described in Patent WO-92 22099, also include microprocessors which are complex and costly systems, and which consume a lot of energy.